1. Field of Invention
The present invention relates to a method and an apparatus for measuring the concentrations of the components of a fluid. More particularly, the present invention relates to a method and an apparatus capable of rapidly and continuously measuring the concentrations of the components of a fluid.
2. Description of Related Art
In various processes of gas production or semiconductor fabrication, it is quite important to be able to control the concentrations of the components of a gas/liquid fluid in real time with a low cost. For example, in a gas separation apparatus, the concentrations of the gas components at its outlet varies as the one at its inlet varies. Therefore those concentrations have to be measured continuously in order to adjust the conditions for gas separation and to control the concentrations of the components of the gas product. Similarly, the concentrations of the components of a fluid need to be measured continuously in other applications that requires controlling the concentrations of gas/liquid components. Particularly, in the field of semiconductor process, the performance of a semiconductor product is relatively dependent on the concentrations of impurities in a high-purity gas being used. If the high-purity gas is contaminated by undesired components or varies in its composition, the yield of the semiconductor products will be reduced significantly.
In the prior art, a component with a relatively high concentration in a gas are analyzed by using gas chromatography (GC) or non-dispersive infrared (NDIR) spectroscopy. However, the GC method can only perform non continuous measurement and can not be used for continuous measurement in real time. Moreover, since the GC method uses a separating column to separate each component of a gas sample, the gas sample to be measured has to be mixed with a carrier gas like helium (He) and therefore can not be reused after the measurement. Consequently, the so-called “in-line monitoring” can not be implemented by using the GC method.
On the other hand, the NDIR spectroscopy can be used for continuous monitoring in real time and is a method frequently used for in-line monitoring. However, since a window made from an IR-transparent material, such as quartz, has to be disposed on the cell of an IR spectrometer, the measuring apparatus for measuring a high-pressure gas is quite bulky. Moreover, since the components to be measured must be IR active, the IR method has the disadvantage that it can not be used to monitor the components IR inactive such as nitrogen (N2) and oxygen (O2), which easily leak into the cell and highly require to be monitored.